b. insertion of a cannula into the external iliac vein
Explanation:
A saphenous cutdown refers to a skin incision associated with insertion of a cannula into the external iliac vein.
It is a more invasive method of exposing the saphenous vein. A cut is made into the skin which is not very deep. A part of vein is exposed which is then cut out for the insertion of cannula. It does not stop the flow of blood, instead it just changes the course. It is also known as the circulatory blood flow.
